Consider the four variables A, B, C and D and a function Z of these variables, Z=15A\(^2\)-3B\(^4\)+C+0.5D It is given that A, B, C and D must be non-negative integers and that all of the following relationships must hold: i) \(2A+B\leq2\) ii) \(4A+2B+C\leq12\) iii) \(3A+4B+D\leq15\) If Z needs to be maximised, then what value must D take?